Protect tab focus chain from infinite loops when item is invisible

Make sure to start the search for a potential focus item on an item that
will be visited again later, otherwise we'll loop for ever.

Fixes: QTBUG-68271
Change-Id: Icb330e4e726132511810027a33b9fb346c7fa131
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@qt.io>

1 files changed, 13 insertions, 2 deletions

diff --git a/src/quick/items/qquickitem.cpp b/src/quick/items/qquickitem.cpp
index 6b5d595c26..8e2d32a818 100644
--- a/src/quick/items/qquickitem.cpp
+++ b/src/quick/items/qquickitem.cpp
@@ -2566,8 +2566,19 @@ QQuickItem* QQuickItemPrivate::nextPrevItemInTabFocusChain(QQuickItem *item, boo
             from = item->parentItem();
     }
     bool skip = false;
-    QQuickItem * startItem = item;
-    QQuickItem * firstFromItem = from;
+
+    QQuickItem *startItem = item;
+    // Protect from endless loop:
+    // If we start on an invisible item we will not find it again.
+    // If there is no other item which can become the focus item, we have a forever loop,
+    // since the protection only works if we encounter the first item again.
+    while (startItem && !startItem->isVisible()) {
+        startItem = startItem->parentItem();
+    }
+    if (!startItem)
+        return item;
+
+    QQuickItem *firstFromItem = from;
     QQuickItem *current = item;
     qCDebug(DBG_FOCUS) << "QQuickItemPrivate::nextPrevItemInTabFocusChain: startItem:" << startItem;
     qCDebug(DBG_FOCUS) << "QQuickItemPrivate::nextPrevItemInTabFocusChain: firstFromItem:" << firstFromItem;